1. Field of the Invention
This invention relates to a lead frame to be used for a semiconductor package device, and a method for its production. More particularly, it is concerned with such lead frame with improved reliability, one part of which is constructed with a resin material.
2. Description of Prior Art
In general, a lead frame for use in a semiconductor package is made by punching with a pressing machine or by etching of a plate material composed of a copper alloy or an iron alloy. In other words, a lead frame to be used in one semiconductor package is constituted with a single kind of metal.
In particular, however, for an integrated circuit package, there have been proposed various types such as one, in which a member made of a metal material is joined with a member made of a resin material, or one, in which a plurality of members, each being made of different kind of metal materials, are joined together, or combined types of these, not to construct the lead frame for use in a single package with one and same metal material, for the reasons to be derived from various factors such as size reduction and versatility of the packages in recent years, increase in the size of integrated circuit elements and the number of input/output terminals, and so forth.
In an attempt to appropriate a single lead frame for the integrated circuit elements in varying sizes, there has been proposed, for example, in the package of ASIC (Application Specific IC), etc., a lead frame of a type, in which a member for mounting thereon the integrated circuit elements (element-mounting member) is constructed with a resin film, in place of using metal, which is glued to the inner leads.
Also, in ZIP (zig-zag inline package) of 4 M DRAM, etc., as the size of the integrated circuit elements becomes very large against the limitation of the package size, routing of the inner lead becomes difficult. On account of this, there has been made publicly known a lead frame of a type such that the resin film as the element-mounting member is joined with the inner leads, on which resin film the integrated circuit elements are mounted and glued.
Further, with increase in power consumption accompanied by increase in the size of the integrated circuit element as well as in the degree of integration, heat-generating quantity increases during the operations of the integrated circuit, with the consequent apprehension such that heat dissipation becomes insufficient in the conventional packages, in general, and the temperature of the elements progressively rises to become the factors of the erroneous operations and disorders in the integrated circuit elements. In a package where the heat dissipation becomes a problem, e.g., in such package that is called power QFP (Quad Flat Package), as an example, there has been published a lead frame of a structure, in which a metal plate of good heat conductivity is used for an element mounting member, with which inner leads are glued together by way of a resin material.
Various constructions exist for such a lead frame, and the basic structure is that a member made of a metal material and a member made of a resin material are joined together by gluing or pressing under heat, and that has a typical cross-sectional profile as shown in FIG. 5 of the accompanying drawing. In this drawing, a reference numeral 1 designates an inner lead constituting a part of the lead frame made of a copper alloy or an iron alloy; a numeral 2 refers to a resin film composed of a resin material such as polyimide, etc.; and a numeral 3 denotes a resin type adhesive agent to join the inner lead 1 with the resin film 2. Further, the resin film 2, as an element-mounting member, joins a semiconductor element 4 with the resin type adhesive agent 3, thereby wire-bonding both the semiconductor element 4 and the inner lead 1 with a thin metal wire 5 to be electrically connected.
As mentioned above, the conventional lead frame is of such a construction that the resin film 2 is directly joined with the inner lead 1 made of a copper alloy or an iron alloy by means of the resin type adhesive 3. In general, however, the adhesive force between the resin type adhesive agent and these metal materials is not necessarily sufficient. On account of this, it is apprehended that, due to shear stress to be exerted at the time of bending work of the lead during the assembling step of the semiconductor package, or thermal stress to be applied under various heating environment, or else, adhesiveness at the above-mentioned adhesive interface becomes decreased to bring about very fine gaps between them. In such case, when moisture-adsorption takes place in the package, water is condensed in these small gaps, and this condensed water, when heated again, becomes vaporized to expand its volume to lead to a possible danger of bringing about cracks in the semiconductor package. Therefore, improvement in the adhesive force between the resin member and the metal member is of paramount importance on the operational reliability of the semiconductor package.